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engine shudder

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Darryl Braun

Joined: 05 May 2006
Posts: 4
Location: Cold Lake

Posted: Tue May 09, 2006 4:43 am Post subject: engine shudder

I have a situation I hope someone can shed some light on.  I'm running a

912 with a 3 blade Warp Drive prop on a 94 Ultravia Pelican PL.  If I pitch

the prop for climb and throttle back at altitude I'll get an occasional

engine shudder.  It actually feels more like someone hit the engine mount

with a hammer or something, just a quick thump.  The engine never misses a

beat.  I've tried 2 and 3 blade wood props and finally the Warp Drive to no

avail.  I've found that keeping a course pitch on the prop kills the proplem

completely during cruise, but I'd like to be able to pitch for climb on hot

days.  When set to a course pitch I can still get the shudder if I decend

too fast with out throttling back.  So basically if the engine isn't working

very hard it tends to have this problem.  If I keep it working hard... no

problem.  I've synced the carbs at every oil change and had the PSRU

inspected and nothing changed.  I've talked to my mechanic and even to Rotax

and they don't know what the deal is.  Anyone out there know what's going

on?



Darryl Braun

Ultravia Pelican PL

C-GGVS

Cold Lake

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_________________
Darryl Braun
94 Pelican PL #583, C-GGVS
Rotax 912

rholder(at)avnet.co.uk
Guest

Posted: Tue May 09, 2006 6:33 am Post subject: engine shudder

Darryl Braun wrote:



 	  Quote: 	
		   I have a situation I hope someone can shed some light

 on.  I'm running a 912 with a 3 blade Warp Drive prop

 on a 94 Ultravia Pelican PL.  If I pitch the prop for

 climb and throttle back at altitude I'll get an

 occasional engine shudder.  It actually feels more like

 someone hit the engine mount with a hammer or

 something, just a quick thump.  The engine never misses

 a beat.  I've tried 2 and 3 blade wood props and

 finally the Warp Drive to no avail.  I've found that

 keeping a course pitch on the prop kills the proplem 

 completely during cruise, but I'd like to be able to

 pitch for climb on hot days.  When set to a course

 pitch I can still get the shudder if I decend too fast

 with out throttling back.  So basically if the engine

 isn't working very hard it tends to have this problem.

 If I keep it working hard... no problem.  I've synced

 the carbs at every oil change and had the PSRU 

 inspected and nothing changed.  I've talked to my

 mechanic and even to Rotax and they don't know what the

 deal is.  Anyone out there know what's going on?


	


I would bet that the engine DOES miss a beat, one or two !



if it happens at the top of the climb when you reduce

power for the cruise then it could well be fuel

vaporization. How close to the exhaust does your fuel pipe

to each carb go ? In the climb there is enough fuel

flowing to avoid the problem. then Immediately after

reducing power everything is "climb-hot" and and the fuel

is flowing slowly -> gets hot -> vaporises -> misfire !

Which stops after 30 seconds or so.



I had this and it took me 6 months to find it ! I run my

fuel pipes to the carb _over_ the carb now, rather than

underneath/ You need a made up union as the banjo won't

move to allow an upwards pipe. Even pointing the banjos

rearward - away from the exhaust - might help !



A hiccup in the cruise after many minutes is most likely

to be carb ice.



I assume it is not a continuous problem so it won't be

anything to do with the prop ! (Famous last words - sorry !)



Richard

G-OWWW Europa 912S Airmaster

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Darryl Braun

Joined: 05 May 2006
Posts: 4
Location: Cold Lake

Posted: Tue May 09, 2006 8:14 pm Post subject: engine shudder

Thanks Richard



Unfortunately it's not carb ice or vapor lock.  It will happen from -20 to

+30 and my fuel lines are all on top of the engine.  It's something related

to how hard the engine works.  If the engine is turning the prop then it's

smooth as silk... if the prop is turning the engine (or the engine is just

not working hard) I get a little kick in the pants every few minutes, and it

is continuous.  I'll keep looking into it and try to record some more data

on when it happens.  It seems like a harmonic vibration between the engine

and the prop, but after 3 different props I know that's not it.  I'm

wondering if it's ignition.  The engine doesn't want to loaf but works well

under load.  My truck was doing almost the same thing and it turned out to

be bad plug wires.



If you can think of anything else or hear of anything, please let me know.



Thanks again.



Darryl Braun

Ultravia Pelican PL

C-GGVS

Cold Lake



--

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_________________
Darryl Braun
94 Pelican PL #583, C-GGVS
Rotax 912

mctrader(at)bigpond.net.a
Guest

Posted: Wed May 10, 2006 1:24 am Post subject: Engine Shudder

Hi Darryl,



Seeing as it only happens when you are off full throttle and on over-run (

prop driving engine rather than the other way around) it sounds to me like

the engine is running too lean. It could also be running too rich, but I

know my 912 would backfire into the muffler whenever I ran a tank dry.

Check the float levels and security of the carburetor needles,



Cheers



Martin in Oz



     1. 05:43 AM - engine shudder  (Darryl Braun)

     2. 07:33 AM - Re: engine shudder  (Richard Holder)

     3. 09:14 PM - Re: engine shudder  (Darryl Braun)



________________________________  Message 1

_____________________________________

Time: 05:43:13 AM PST US

From: "Darryl Braun" <dvbraun(at)telus.net>

Subject: engine shudder






  I have a situation I hope someone can shed some light on.  I'm running a

912 with a 3 blade Warp Drive prop on a 94 Ultravia Pelican PL.  If I pitch

the prop for climb and throttle back at altitude I'll get an occasional

engine shudder.  It actually feels more like someone hit the engine mount

with a hammer or something, just a quick thump.  The engine never misses a

beat.  I've tried 2 and 3 blade wood props and finally the Warp Drive to no

avail.  I've found that keeping a course pitch on the prop kills the proplem

completely during cruise, but I'd like to be able to pitch for climb on hot

days.  When set to a course pitch I can still get the shudder if I decend

too fast with out throttling back.  So basically if the engine isn't working

very hard it tends to have this problem.  If I keep it working hard... no

problem.  I've synced the carbs at every oil change and had the PSRU

inspected and nothing changed.  I've talked to my mechanic and even to Rotax

and they don't know what the deal is.  Anyone out there know what's going

on?



Darryl Braun

Ultravia Pelican PL

C-GGVS

Cold Lake

- The Matronics RotaxEngines-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?RotaxEngines-List

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